System and method for generating a phase scintillation map utilized for de-weighting observations from gnss satellites

ABSTRACT

A system and method generates a phase scintillation map that is utilized to de-weight satellite signal observations from GNSS satellites. One or more base stations each assign an index value to one or more GNSS satellite in view, where the index value indicates an adverse effect of ionospheric scintillation on signals received from the GNSS satellite. The values and identifiers may be transmitted to a server. The server utilizes the received information to generate the phase scintillation map that may include one or more scintillation bubbles, wherein a location of each scintillation bubble is based on the received information. The phase scintillation map is transmitted to one or more rovers. The rover determines if a pierce point associated with a selected GNSS satellite in view of the rover falls within the boundaries of a scintillation bubble. If so, satellite signal observations from the selected GNSS satellite are de-weighted.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a division of commonly assigned copendingU.S. patent application Ser. No. 15/679,758 which was filed on Aug. 17,2017, by Thomas Morley for SYSTEM AND METHOD FOR GENERATING A PHASESCINTILLATION MAP UTILIZED FOR DE-WEIGHTING OBSERVATIONS FROM GNSSSATELLITES, which is hereby incorporated by reference.

BACKGROUND Technical Field

The invention relates generally to global navigation satellite systems(GNSS), and in particular, to a system that generates a phasescintillation map that is utilized for de-weighting satellite signalobservations from GNSS satellites.

Background Information

The ionosphere is a layer of the Earth's atmosphere that is ionized bysolar and cosmic radiation and typically lies 75-1000 km (46-621 miles)above the Earth's surface. Particular portions or regions of theionosphere, known as scintillation bubbles, are susceptible toionospheric scintillation which causes radio-frequency signals passingthrough the scintillation bubble to experience rapid fluctuations inphase and/or amplitude. Specifically, global navigation satellite system(GNSS) satellite signals interact with free electrons along thepropagation path through the scintillation bubble causing phase errors,rapid phase fluctuations and/or signal power fading in the receivedsignals, which may result in cycle slips and possible loss of lock at aGNSS receiver and lead to a degradation in overall positioning accuracy.

To account for the adverse effects associated with the ionosphere,traditional approaches may de-weight satellite signal observations(e.g., pseudorange measurements and phase measurement) based on GNSSsatellite elevation and/or GNSS signal carrier-to-noise-density ratio(C/N₀). However, elevation and/or the C/N₀ may not be a good predictorof which of the GNSS satellite signals are being adversely affected bythe ionosphere.

SUMMARY

The inventive system and method generates a phase scintillation map thatis utilized for de-weighting satellite signal observations.Specifically, each base station receives satellite signals from one ormore global navigation satellite systems (GNSS) satellites that are inview of the base station. The base station determines to what extent thesignals received from a GNSS satellite are being adversely affected byatmospheric conditions, specifically, by ionospheric scintillation. Forexample, the base station may assign an index value to a GNSS satelliteindicative of the adverse effect of ionospheric scintillation onsatellite signals transmitted by the GNSS satellite. Specifically, theindex value may indicate to what extent the satellite signals, from theGNSS satellite, are being adversely affected by ionosphericscintillation from a scintillation bubble in the ionosphere. The basestation then transmits the index value and other information to acentral server. The other information may include the coordinates of apierce point. As used herein, the coordinates of a pierce point indicatea location where the satellite signals transmitted by the GNSS satelliteand received by the receiver intersect with the ionosphere.

The central server utilizes the information received from the basestations to generate a phase scintillation map that may include one ormore scintillation bubbles. Specifically, the central server generatesthe phase scintillation map for a particular geographical location,wherein the phase scintillation map may include scintillation bubblesthat are placed at particular locations on the phase scintillation mapbased on the received information. For example, the coordinates of oneor more pierce points determined by the base stations and the indexvalues assigned by the base stations are utilized to determine thelocations of the scintillation bubbles on the phase scintillation map.

The central server then transmits the generated phase scintillation mapto one or more rovers. Each rover may then determine if a pierce pointthat is associated with satellite signals for a given GNSS satellite inthe view of the rover has coordinates that fall within the boundaries ofa scintillation bubble on the phase scintillation map. If thecoordinates of the pierce point fall within the boundaries of thescintillation bubble, the satellite signal observations associated withthe given GNSS satellite may be de-weighted by the rover.

Advantageously, when performing position calculations, the satellitesignal observations (e.g., pseudorange measurements and phasemeasurement) from GNSS satellites that have corresponding pierce pointsthat do not fall within the boundaries of a scintillation bubble areutilized instead of or prioritized over the satellite signalobservations calculated from the GNSS satellites signals that areassociated with pierce points that fall within the boundaries of ascintillation bubble.

BRIEF DESCRIPTION OF THE DRAWINGS

The description below refers to the accompanying drawings, of which:

FIG. 1 illustrates a system in accordance with an illustrativeembodiment of the invention;

FIG. 2 illustrates an exemplary environment in which the system of FIG.1 may operate;

FIG. 3 illustrates an exemplary table that may store values associatedwith the operation of the system of FIG. 1;

FIG. 4 illustrates an exemplary phase scintillation map associated withthe operation of the system of FIG. 1; and

FIG. 5 is an exemplary flow chart for the operation of the systems ofFIG. 1.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

Referring to FIG. 1, a system 100 includes one or more rovers 112, oneor more base stations 116, and a central server 124. The rovers 112 andbase stations 116 may operate as part of a real time kinematic (RTK)system and/or a Precise Point Positioning (PPP) system over a wired orwireless network (not shown), as known by those skilled in the art.

The one or more base stations 116 are typically stationary, have knownpositions and essentially clear views of the sky. Each base station 116includes an antenna 125 that receives global navigation satellite system(GNSS) satellite signals from one or more GNSS satellites 110 in view ofthe base station 116. In addition, the base station 116 includes one ormore processors 118, a memory 119, and an oscillator 121, such as anOvenized Crystal Oscillator (OXCO). It is noted that although oscillator121 is depicted as being a separate component within the base station116, it is expressly contemplated that the oscillator 121 may be part ofionospheric monitoring subsystem 120. The one or more processors 118 mayoperate in a known manner to acquire and track the GNSS satellitesignals, make carrier and phase observations, determine pseudoranges,and determine correction information as known by those skilled in theart.

The base station 116 may output, in a known manner, a variety of signalmeasurements and statistics useful for characterizing the localionospheric condition. Specifically, the base station 116 may sample rawamplitude and phase of each tracked GNSS signal at a particular rate(e.g., 50 Hz). The raw amplitude and phase along with the raw totalelectron content (TEC) measurements, which are computed from acombination of multiple frequencies, are then processed, in a knownmanner, to produce summary logs of scintillation index values and TEC.The base station 116 may calculate, in a known manner, an amplitudescintillation index (S4) value, a phase scintillation index (σ_(φ))value, and the TEC. S4 and σ_(φ) may be computed for each frequency thatbase station 116 tracks (e.g., L1, L2, and L5). Higher values of S4and/or σ_(φ) can be attributed to, for example, an atmosphericcondition, such as, ionospheric scintillation from a scintillationbubble in the ionosphere.

S4 is dimensionless and defined as the square root of the normalizedvariance of signal intensity over a defined period of time. An S4 valueof 0.6 or higher may be associated with strong scintillation, while anS4 value of 0.3 or lower may be associated with weak or no scintillation(e.g., conditions unlikely to have any noticeable impact on receiverperformance).

σ_(φ) is the standard deviation of the received signal phase over adefined period of time and measured in radians or degrees. For example,σ_(φ) may be computed over a plurality of different time intervals. Aσ_(φ) value of 1 radian or higher may be associated with strongscintillation, while a σ_(φ) value of 0.1 radians or lower may beassociated with weak or no scintillation. In addition, although the basestation 116 need not transmit the scintillation information to the rover112, the base station 116 may transmit scintillation information such asthe S4 value, the σ_(φ) value, and/or correction information to therovers 112 in the form of one or more RTK messages and/or PPP messagesas known by those skilled in the art.

The one or more processors 118 are configured to execute the ionosphericmonitoring subsystem 120 that is configured to operate in accordancewith one or more embodiments described herein. Specifically, and asdescribed in further detail below, the ionospheric monitoring subsystem120 may calculate one or more of the S4, the σ_(φ), and/or the TECvalues to indicate to what extent the satellite signals from each GNSSsatellite 110 in view of the base station 116 are being adverselyaffected by the atmospheric condition, and specifically, ionosphericscintillation. For example, the ionospheric monitoring subsystem 120 mayassign to a GNSS satellite 110, based on the S4 or the σ_(φ) values,alone or in combination with the TEC value, an index value indicating towhat extent ionospheric scintillation is adversely affecting the signalsfrom the GNSS satellite 110. The one or more index values and othervalues, as described in further detail below, may be stored in thememory 119 and then transmitted from the base station 116 to the centralserver 124 using a variety of different types of messages. For example,the index values may be broadcast to the central server 124 and/ortransmitted to the central server 124 utilizing any of a variety oftypes of messages.

The central server 124 includes one or more processors 130, a memory132, and one or more network interfaces 136. The network interfaces 136contain the mechanical, electrical, and signaling circuitry forcommunicating with the rovers 112 and base stations 116 over a wired orwireless network (not shown).

The one or more processors 130 execute a phase scintillation mapgenerator subsystem 134 configured to generate a phase scintillation map400 in accordance with one or more embodiments described herein. Inaddition, the memory 132 may store a table 300, which contains one ormore values received from the base stations 116. In addition oralternatively, the table 300 may be stored in storage (not shown) thatis coupled to and external to the central server 124. The storagecoupled to and external to the central server 124 may be, but is notlimited to, a database, storage device such as hard disk drives (HDDs),and/or storage devices such as solid state drives (SSDs). The phasescintillation map generator subsystem 134 may utilize the values storedin the table 300 to generate the phase scintillation map 400, asdescribed in further detail below. In addition, the phase scintillationmap may be transmitted from the central server 124 to one or more rovers112. For example, the phase scintillation map 400 may be broadcast tothe one or more rovers 112 and/or transmitted to the one or more rovers112 utilizing any of a variety of types of messages.

The rover 112 includes an antenna 115, one or more processors 113, and amemory 114. The one or more processors 113 determine positions based onthe timing of codes and carriers in the received satellite signalsreceived at antenna 115 as known by those skilled in the art. The one ormore processors 113 execute a pierce point calculation subsystem 117configured to operate in accordance with one or more embodimentsdescribed herein. The memory 114 may store the phase scintillation mapgenerated by and received from the central server 124, as described infurther detail below.

FIG. 2 shows an environment in which the system of FIG. 1 may operate.As depicted in FIG. 2, a GNSS satellite 110 a (hereinafter “SatelliteA”) is in view of base stations 116 a and 116 b, and a GNSS satellite110 b (hereinafter “Satellite B”) is in view of base station 116 b. Inthe example as depicted in FIG. 2, Satellite B is not in view of thebase station 116 a. The signals transmitted by Satellite A and SatelliteB are indicated by the lines labeled as propagation paths A, B, and C inFIG. 2. Although Satellite A is at a higher elevation than Satellite Bin FIG. 2, the satellite signals transmitted by Satellite A and receivedby the base stations 116 a and 116 b are adversely affected byionospheric scintillation of the scintillation bubble 202, while thesignals transmitted by Satellite B and received by the base station 116b are not adversely affected by ionospheric scintillation of thescintillation bubble 202.

Specifically, scintillation bubble 202, which is in the signal pathsfrom Satellite A to the respective base stations 116 a and 116 bsubjects the signals to ionospheric scintillation. As such, the signalsfrom Satellite A to the base stations 116 a and 116 b interact with freeelectrons of the scintillation bubble 202 along the associatedpropagation paths (e.g., propagation paths A and B), causing phaseerrors, rapid phase fluctuations and/or signal power fading in thereceived signals, which may result in cycle slips and possible loss oflock at the receiver and lead to a degradation in overall positioningaccuracy.

In operation, the respective base stations 116 a and 116 b measure TECand analyze amplitude and phase measurements to calculate the S4 and/orthe σ_(φ) values for each of the satellite signals received fromrespective GNSS satellites at one or more different frequencies (e.g.,L1, L2, and L5). Using one or more of the S4, and σ_(φ), and TEC valuesthe base station 116 then determines the extent of adverse effect ofionospheric scintillation on the satellite signals. A determination oflow or minimal S4 values (e.g., 0.03 or lower) or low or minimal σ_(φ)values (e.g., 0 radian or 0.1 radian), alone or in combination with theTEC value, may indicate that the satellite signals received from aparticular GNSS satellite are not being adversely affected byionospheric scintillation (i.e., weak or no ionospheric scintillation).Small S4 values (e.g., between 0.4 and 0.6) or σ_(φ) values (e.g.,between 0.2 to 0.9 radian) alone or in combination with the TEC valuemay indicate that the satellite signals from a particular GNSS satelliteare being adversely affected, to a small extent, by ionosphericscintillation (i.e., weak ionospheric scintillation). Large S4 values(e.g., 0.6 or higher) or σ_(φ) values (e.g., 1 radian or higher) aloneor in combination with the TEC value may indicate that the satellitesignals from a particular GNSS satellite are being adversely affected,to a large extent, by ionospheric scintillation (i.e., strongionospheric scintillation). Therefore, as the S4 or the σ_(φ) valueincrease, the ionospheric monitoring subsystem 120 of the base station116 determines that the adverse effect of ionospheric scintillation onthe signals from the GNSS satellite is getting stronger.

In accordance with one or more embodiments described herein, the basestation 116 may assign a particular index value of an index scale to aparticular GNSS satellite 110 based on the calculated S4 or the σ_(φ)value alone or in combination with the TEC value. For example, if theindex scale is 0 to 5, the ionospheric monitoring subsystem 120 of thebase station 116 may assign an index value of 0 when the S4 or the σ_(φ)value alone or in combination with the TEC value is equal to or below alower threshold value, indicating that the satellite signals from aparticular GNSS satellite are not being adversely affected byionospheric scintillation (i.e., no ionospheric scintillation). In theexample, an exemplary lower threshold value may be 0.3 for S4 and 0.1radians for σ_(φ). In addition, the ionospheric monitoring subsystem 120of the base station 116 may assign an index value of 5 when the S4 orthe σ_(φ) value alone or in combination with the TEC value is equal toor greater than a higher threshold value, indicating that the signalsfrom the GNSS satellite are being adversely affected, to a large extent,by ionospheric scintillation (i.e., strong ionospheric scintillation).In the example, an exemplary higher threshold value may be 0.6 for S4and 1 radian for σ_(φ).

Further, for any S4 or the σ_(φ) value alone or in combination with theTEC value that are between the lower and higher threshold values,indicating that the signals from the GNSS satellite are being adverselyaffected, to a certain extent, by ionospheric scintillation, theionospheric monitoring subsystem 120 of the base station 116 mayrespectively assign different index values of 1, 2, 3, or 4. Forexample, if the S4 or the σ_(φ) value alone or in combination with theTEC value is close to and above the lower threshold value, theionospheric monitoring subsystem 102 may assign an index value of 1 tothe GNSS satellite (i.e., weak ionospheric scintillation). Similarly, ifthe S4 or the σ_(φ) value alone or in combination with the TEC value isclose to yet still below the higher threshold value, the ionosphericmonitoring subsystem 120 may assign an index value of 4 to the GNSSsatellite. As such, the assigned index values indicate to what extentthe satellite signals from a particular GNSS satellite are adverselyaffected by ionospheric scintillation. In addition, and in a knownmanner, the base station 116 may determine the coordinates of a piercepoint (e.g., x, y, and/or z coordinates where the satellite signals of aparticular GNSS satellite to the base station intersects with theionosphere) for each GNSS satellite in view of the base station 116.

Thus, the base stations 116 a and 116 b assign index values to each GNSSsatellite in view and determine coordinates for corresponding piercepoints for each GNSS satellite. The use of an index scale from 0 to 5with respect to FIG. 2 is for illustrative purposes and it is expresslycontemplated than any scale may be utilized and any values or indicatorsmay be assigned to the GNSS satellites to indicate to what extent thesatellite signals from the GNSS satellites are being adversely affectedby ionospheric scintillation based on the calculated S4 or the σ_(φ)value alone or in combination with the TEC value.

In the example as depicted in FIG. 2, the scintillation bubble 202 ofthe ionosphere 201 is in the path (e.g., propagation path A) of thesatellite signals transmitted by Satellite A and received by the basestation 116 a. Further and in this example, the S4 or the σ_(φ) valuedetermined by base station 116 a based on the satellite signals receivedfrom Satellite A at the L1 frequency is greater than the higherthreshold value. Thus, the ionospheric monitoring subsystem 120 of basestation 116 a assigns an index value of 5 to Satellite A. In addition,the processor 118 of base station 116 a determines the coordinates forpierce point 203 a, where the coordinates indicate where the satellitesignals (indicated by propagation path A) from Satellite A intersectwith the ionosphere 201. Specifically, the processor 118 of base station116 a determines coordinates for pierce point 203 a to be x₁, y₁, andz₁.

Further and based on the example as depicted in FIG. 2, thescintillation bubble 202 of the ionosphere 201 is in the path (e.g.,propagation path B) of the satellite signals transmitted by Satellite Aand received by the base station 116 b. In addition and for thisexample, the S4 or the σ_(φ) value determined by base station 116 bbased on the satellite signals received from Satellite A at the L1frequency is between the lower threshold value and the higher thresholdvalue. Thus, the ionospheric monitoring subsystem 120 of base station116 b may assign an index value of 3 to Satellite A based on thesatellite signals from GNSS satellite 110 passing through thescintillation bubble 202 at a particular point with relation to thecenter and edge of the scintillation bubble 202. In addition, and in aknown manner, the processor 118 of base station 116 b determines thecoordinates for pierce point 203 b to be the x₂, y₂, and z₂.

In addition and based on the example as depicted in FIG. 2, thescintillation bubble 202 of the ionosphere 201 is not in the path (e.g.,propagation path C) of the signals transmitted from Satellite B andreceived by the base state 116 b at the L1 frequency. Thus, and based onthe calculated S4 or σ_(φ) value being less than or equal to the lowerthreshold value, the ionospheric monitoring subsystem 120 of basestation 116 b assigns an index value of 0 to Satellite B. In addition,and in a known manner, the processor 118 of base station 116 bdetermines the coordinates for pierce point 203 c to be x₃, y₃, and z₃.

Although FIG. 2 depicts Satellite A being in view of base stations 116 aand 116 b and Satellite B being in view of only base station 116 b, itis expressly contemplated that any number of GNSS satellites may be inview of each base station, and the base stations may assign particularindex values to each of the GNSS satellites in view of the basestations, in a similar manner as described herein.

Base stations 116 a and 116 b may then transmit one or more values andidentifiers to the central server 124 for inclusion in, for example, thetable 300. Specifically, the values and identifiers transmitted frombase stations 116 a and 116 b to the central server 124, may include,but are not limited to, a base station identifier, a GNSS satelliteidentifier, a pierce point location (e.g., coordinates values), anassigned index value, and the frequency being tracked. For example, basestations 116 a and 116 b may broadcast the values and identifiers to thecentral server 124.

FIG. 3 depicts the table 300 that may be used to store the particularvalues and identifiers transmitted from the base station 116 to thecentral server 124. The table 300 may be stored in the memory 132 of thecentral server 124 and/or storage (not shown) coupled to the centralserver 124. It should be noted that the use of a table is forillustrative purposes, and in alternative embodiments a different datacontainer or structure may be utilized. The table 300 may include a basestation identifier column 302, a GNSS satellite identifier column 304, apierce point location column 306, an assigned index value column 308,and a frequency column 310. The base station identifier column 302 maystore an identifier that uniquely identifies a base station. The GNSSsatellite identifier column 304 may store an identifier that uniquelyidentifies a GNSS satellite. The pierce point location column 306 maystore the x, y, and/or z coordinates determined for a pierce point. Theassigned index value column 308 may store an index value assigned to aGNSS satellite by a base station, and the frequency column 310 may storethe frequency being tracked by a base station when the base stationcalculates the S4 or the σ_(φ) value alone or in combination with theTEC value.

For example, the table 300 may store the values determined and assignedas described above in reference to the example in FIG. 2. Specifically,the base station identifier column 302 may store a base stationidentifier of “Base Station A” for base station 116 a. In addition, andin a corresponding row entry, the GNSS satellite identifier column 304may store a GNSS identifier of “Satellite A” for GNSS satellite 110 a.Further, in another corresponding row entry, the pierce point locationcolumn 306 may store x₁, y₁, and z₁ coordinates for pierce points 203 a.In another corresponding row entry, the assigned index value column 308may store the index value of 5 assigned by base station 116 a indicatingthat the signals from Satellite A are being adversely affected, to alarge extent, by ionospheric scintillation. Finally, in anothercorresponding row entry, the frequency column 310 may store the value ofL1 indicating the frequency being tracked by base station 116 a.

In a different row, the base station identifier column 302 may store abase station identifier of “Base Station B” for base station 116 b. Inaddition, and in a corresponding row entry, the GNSS satelliteidentifier column 304 may store a GNSS identifier of “Satellite A” forGNSS satellite 110 a. Further, in another corresponding row entry, thepierce point location column 306 may store x₂, y₂, and z₂ coordinatesfor pierce points 203 b. In another corresponding row entry, theassigned index value column 308 may store the index value of 3 assignedby base station 116 b indicating that the satellite signals fromSatellite A are being adversely affected by ionospheric scintillation.Finally, in another corresponding row entry, the frequency column 310may store the value of L1 indicating the frequency being tracked by basestation 116 b.

Similarly and in another different row, the base station identifiercolumn 302 may store a base station identifier of “Base Station B” forbase station 116 b. In addition, and in a corresponding row entry, theGNSS satellite identifier column 304 may store a GNSS identifier of“Satellite B” for GNSS satellite 110b. Further, in another correspondingrow entry, the pierce point location column 306 may store x₃, y₃, and z₃coordinates for pierce points 203 c. In another corresponding row entry,the assigned index value column 308 may store the index value of 0assigned by base station 116 b indicating that the satellite signalsfrom Satellite B are not being adversely affected by ionosphericscintillation. Finally, in another corresponding row entry, thefrequency column 310 may store the value of L1 indicating the frequencybeing tracked by base station 116 b.

Thus, and as more base stations 116 provide assigned values andinformation to the central server 124, the central server 124 may storethose values in the table 300 to more accurately determine the extent ofionospheric scintillation in the ionosphere and more accuratelydetermine where the scintillation bubbles are located. It is noted thatthe values stored in the table 300 are for illustrative purposes andother and/or differing values may be stored in the table 300. Forexample, although reference is made to base stations 116 a assigning aparticular index value to Satellite A, it expressly contemplated thatbase station 116 a may assign any of a variety of values or indicatorsto one or more other satellites 110 in view of base station 116 a to bestored in the table 300. In addition, although reference is made to basestations 116 a and 116 b tracking the L1 frequency, it is expresslycontemplated that base stations 116 a and 116 b may track otherfrequencies or a plurality of frequencies (e.g., L2, L5, etc.).

FIG. 4 is a phase scintillation map 400 generated in accordance with oneor more embodiments described herein. Specifically, the processor 130 ofthe central server 124 executes the phase scintillation map generatorsubsystem 134 to utilize the values stored in the table 300 to generatethe phase scintillation map 400. More specifically, and by utilizing thelocation of the pierce points 203 together with the identifiers andindex value assigned to given GNSS satellites in view of a base station116 and stored in table 300, the phase scintillation map generatorsubsystem 134 may generate the phase scintillation map 400 indicatingwhere the scintillation bubbles are located.

For example, a first, second, and third base station 116 may all have aview of a given GNSS satellite and the three base stations mayrespectively assign index values of 1, 5, and 1 to the given GNSSsatellite 110 in the manner described above. In addition, the first basestation may have an associated pierce point 404 a at a first set ofcoordinates, the second base station may have an associated pierce point404 b at a second set of coordinates, and the third base station mayhave an associated pierce point 404 c at a third set of coordinates.Therefore, the phase scintillation map generator subsystem 134 maydetermine that scintillation bubble 402 a has its center at thecoordinates associated with the second pierce point 404 b that wasassigned a value of 5, and that scintillation bubble 402 a attenuates orhas its edge at the coordinates associated with the first pierce point404 a and third pierce point 404 c that were assigned an index valueof 1. Therefore, ionospheric scintillation at the center ofscintillation bubble 402 a is strong, while ionospheric scintillation atthe edges of scintillation bubble 402 a is weak.

Alternatively, and if the first and third base stations both assignedindex values of 5, the scintillation bubble 402 a may be at the samelocation and may have the same shape and size, however ionosphericscintillation would be uniform and strong at the center and at the edgesof scintillation bubble 402 a.

FIG. 4 shows phase scintillation map that includes the scintillationbubble 402 a and also includes a second scintillation bubble 402 b. Thescintillation bubbles 402 a and 402 b are positioned at particularpoints with respect to True North (hereinafter “N”) 404. Although thephase scintillation map 400 as depicted in FIG. 4 includes twoscintillation bubbles 402 a and 402 b, it is expressly contemplated thatthe phase scintillation map 400 may include any number of scintillationbubbles that may be of any shape and size, and may be located anywhereon the phase scintillation map 400 based on the values received from theone or more base stations 116 and stored in the table 300. In addition,it is expressly contemplated that a single phase scintillation map 400may be generated for each frequency or a single phase scintillation map400 may be generated for a plurality of frequencies. As such, theexample as described with respect to FIG. 4 is for illustrativepurposes, and any assigned index values, identifiers, and pierce pointlocations may be utilized to determine the shape, size and location of ascintillation bubble.

In addition, it is noted that scintillation bubbles are not stationaryand move through the ionosphere over time. As such, the phasescintillation map 400 may be updated at one or more particular times toaccount for the movement of the scintillation bubbles.

The central server 124 may then transmit the phase scintillation map 400to one or more rovers 112. Each rover 112 may utilize the phasescintillation map 400 to determine if a pierce point determined by therover for a given GNSS satellite in view of the rover 112 falls withinthe boundaries of a scintillation bubble of the phase scintillation map400. For example, the pierce point calculation subsystem 117 of therover 112 may determine that the coordinates of a pierce point,associated with the given GNSS satellite in view of the rover 112, arex₄, y₄, and z₄. The pierce point calculation subsystem 117 may thencompare the coordinates of the pierce point with the locations ofscintillation bubbles 402 a and 402 b to determine if the coordinatesfall within the boundaries of scintillation bubble 402 a or 402 b of thephase scintillation map 400.

If the rover 112 determines that the coordinates of the pierce point(e.g., x₄, y₄, and z₄) associated with a given GNSS satellite fallwithin the boundaries of scintillation bubble 402 a or 402 b of thephase scintillation map 400, the pierce point calculation subsystem 117may de-weight the satellite signal observations (e.g., pseudorangemeasurements and phase measurements) for the given GNSS satellite. Forexample, the pierce point calculation subsystem 117 may assign a weightof 0 to the satellite signal observations for the given GNSS satellite.In addition, the pierce point calculation subsystem 117 may assign aweight of 1 to the satellite signal observations for a given GNSSsatellite that has a corresponding pierce point that falls outside ofthe boundaries of scintillation bubble 402 a or 402 b of the phasescintillation map 400. As such and when performing positioncalculations, the satellite signal observations for GNSS satellites thathave corresponding pierce points that fall outside the boundaries of ascintillation bubble (i.e., the satellite signal observations that areassigned a weight of 1) are utilized instead of or prioritized over thesatellite signal observations for the GNSS satellites that havecorresponding pierce points that fall within the boundaries of ascintillation bubble (i.e., the satellite signal observations that areassigned a weight of 0).

In an alternative embodiment, the rover 112 may assign a particularweight to the satellite signal observations for a given GNSS satellitebased on the pierce point being located at a particular position withinscintillation bubble of the phase scintillation map. For example andassuming a scale of 0 to 1, the rover 112 may assign a weight of 0 tothe satellite signal observations for the given GNSS satellite if thepierce point associated with the given GNSS satellite is located at aposition within scintillation bubble 402 a or 402 b where there isstrong ionospheric scintillation (e.g., at the center of scintillationbubble 402 a of the phase scintillation map 400). In addition, the rover112 may assign a weight of 0.5 based on the pierce point beingpositioned somewhere between the center and edge of scintillation bubble402 a or 402 b of the phase scintillation map 400. Further, the rover112 may assign a weight of 1 based on pierce point being outside ofscintillation bubble 402 a or 402 b of the phase scintillation map 400.As such and when performing position calculations, satellite signalobservations for GNSS satellites associated with no ionosphericscintillation or weak ionospheric scintillation may be prioritized oversatellite signal observations for GNSS satellites associated with strongionospheric scintillation.

Although reference is made to assigning particular weights to thesatellite signal observations to de-weight the satellite signalobservations, it is expressly contemplated that the satellite signalobservations, for a given GNSS satellite having a corresponding piercepoint within a scintillation bubble of a phase scintillation map, may bede-weighted in any of a variety of ways and as known by those skilled inthe art.

FIG. 5 is an exemplary flow chart of the operation of the system andmethod for generating a phase scintillation map utilized forde-weighting satellite signal observations. The procedure 500 starts atstep 505 and continues to step 510, where one or more base stationsassign an index value to GNSS satellites in view of the base station.Specifically, the ionospheric monitoring subsystem 120 of the basestation 116 assigns a value to each GNSS satellite 110 in view of thebase station 116 based on the calculated S4 or the σ_(φ) value alone orin combination with the TEC value. The index value assigned to each GNSSsatellite indicates the severity of the adverse effects of ionosphericscintillation on satellite signals transmitted by the GNSS satellite.

The procedure continues to step 515 where a central server receives theindex values assigned to the GNSS satellites and other information fromthe one or more base stations. The other information may include, but isnot limited to, a unique identifier identifying the base station, aunique identifier for the GNSS satellite in view of the base station,coordinates for the pierce point associated with the GNSS satellite inview of the base station, and the frequency being tracked by the basestation. The assigned index values and other information may be storedin table 300.

The procedure continues to step 520 where the central server generates aphase scintillation map utilizing the received index values and otherinformation. Specifically, the phase scintillator map generatorsubsystem 134 generates a phase scintillation map 400 that includes oneor more scintillation bubbles, wherein the location of the respectivescintillation bubbles are based on the received assigned index valuesand the other information.

The procedure continues to step 525 where the phase scintillation map istransmitted to one or more rovers. For example, the central server 124broadcasts the phase scintillation map 400 to one or more rovers 112.The procedure continues to step 530 where satellite signal observationsare de-weighted based on the phase scintillation map. Specifically, thesatellite signal observations are de-weighted should the rover determinethat one or more pierce points, determined for one or more GNSSsatellites in view of the rover, fall within the boundaries of thescintillation bubbles on the phase scintillation map.

More specifically, the pierce point calculation subsystem 117 of therover 112 determines the coordinates for a pierce point associated witha given GNSS satellite in view of the rover 112. The pierce pointcalculation subsystem 117 then compares the coordinates of the piercepoint with the location of the scintillation bubbles on the phasescintillation map to determine if the coordinates fall within theboundaries of a scintillation bubble. If the coordinates of the piercepoint associated with the given GNSS satellite fall within theboundaries of a scintillation bubble of the phase scintillation map 400,the satellite signal observations from the given GNSS satellite arede-weighted.

For example, the satellite signal observations from the given GNSSsatellite having a corresponding pierce point that falls within theboundaries of a scintillation bubble of the phase scintillation map maybe assigned a particular weight less than 1, or less than a maximumweight, to de-weight the satellite signal observations for use inposition calculations.

The procedure continues to step 535 where the rover performs positioncalculations based on the de-weighting of the satellite signalobservations. Therefore and when performing position calculations, thesatellite signal observations for GNSS satellites that havecorresponding pierce points that fall outside the boundaries of ascintillation bubble are utilized instead of or prioritized over thesatellite signal observations for the GNSS satellites that havecorresponding pierce points that fall within the boundaries of ascintillation bubble.

The foregoing description described certain example embodiments. It willbe apparent, however, that other variations and modifications may bemade to the described embodiments, with the attainment of some or all oftheir advantages. For example, although reference is made to the centralserver receiving the assigned index values and other information fromthe base stations to generate the phase scintillation map, it isexpressly contemplated that a selected base station may receive theassigned index values and other information from other base stations andthe selected base station may generate the phase scintillation map andtransmit the phase scintillation map to the one or more rovers in themanner described above. In addition, the base stations 116 may send theS4, the σ_(φ), and/or the TEC values to the central server 112 and thecentral server 124 may assign an index value and calculate a piercepoint for the base station 116 in the manner described above.Accordingly, the foregoing description is to be taken only by way ofexample, and not to otherwise limit the scope of the disclosure. It isthe object of the appended claims to cover all such variations andmodifications as come within the true spirit and scope of thedisclosure.

What is claimed is:
 1. A rover, comprising: a processor and a memory,the processor configured to: receive, from a server, a phasescintillation map including one or scintillation bubbles, wherein alocation of each scintillation bubble on the phase scintillation map isbased on coordinates of one or more base station pierce points and oneor more assigned index values; determine if a pierce point, associatedwith a selected global navigation satellite systems (GNSS) satellite inview of the rover, falls within boundaries of a scintillation bubble ofthe one or more scintillation bubbles of the received phasescintillation map; de-weight selected satellite signal observationsassociated with satellite signals transmitted by the selected GNSSsatellite in response to determining the pierce point falls within theboundaries of the scintillation bubble; and perform one or more positioncalculations in response to the selected satellite signal observationsbeing de-weighted.
 2. The rover of claim 1, wherein each base stationpierce point corresponds to a particular GNSS satellite and each indexvalue indicates an adverse effect of ionospheric scintillation onsatellite signals transmitted by the particular GNSS satellite.
 3. Therover of claim 1, wherein the processor is further configured to:exclude the selected satellite signal observations when performing theposition calculations.
 4. The rover of claim 1, wherein the processor isfurther configured to: prioritize particular satellite signalobservations associated with one or more other GNSS satellites over theselected satellite signal observations when performing the positioncalculations.
 5. The rover of claim 1, wherein the one or more assignedindex values are based on at least one of an amplitude scintillationindex (S4) value and a phase scintillation index (σ_(φ)).
 6. The roverof claim 1, wherein the processor is further configured to: assign afirst weight to a first selected observation associated with thesatellite signals transmitted by the selected GNSS satellite in responseto determining the pierce point falls within the boundaries of thescintillation bubble; and assign a second weight to the first selectedobservations associated with the satellite signals transmitted by theselected GNSS satellite in response to determining the pierce point doesnot fall within the boundaries of the scintillation bubble.
 7. The roverof claim 1, wherein the processor is further configured to: assign afirst weight to a first selected observation associated with thesatellite signals transmitted by the selected GNSS satellite in responseto determining the pierce point is at a first location within theboundaries of the scintillation bubble; and assign a second weight tothe first selected observations associated with the satellite signalstransmitted by the selected GNSS satellite in response to determiningthe pierce point is at a second location within the boundaries of thescintillation bubble, wherein the first location and the second locationare different locations.
 8. A method, comprising: receiving, at a roverand from a server, a phase scintillation map including one orscintillation bubbles, wherein a location of each scintillation bubbleon the phase scintillation map is based on coordinates of one or morebase station pierce points and one or more assigned index values;determining, by a processor of the rover, if a pierce point, associatedwith a selected global navigation satellite systems (GNSS) satellite inview of the rover, falls within boundaries of a scintillation bubble ofthe one or more scintillation bubbles of the received phasescintillation map; de-weighting, by the processor, selected satellitesignal observations associated with satellite signals transmitted by theselected GNSS satellite in response to determining the pierce pointfalls within the boundaries of the scintillation bubble; and performingone or more position calculations in response to the selected satellitesignal observations being de-weighted.
 9. The method of claim 8, whereineach base station pierce point corresponds to a particular GNSSsatellite and each index value indicates an adverse effect ofionospheric scintillation on satellite signals transmitted by theparticular GNSS satellite.
 10. The method of claim 8, furthercomprising: excluding the selected satellite signal observations whenperforming the position calculations.
 11. The method of claim 8, furthercomprising: prioritizing particular satellite signal observationsassociated with one or more other GNSS satellites over the selectedsatellite signal observations when performing the position calculations.12. The method of claim 8, wherein the one or more assigned index valuesare based on at least one of an amplitude scintillation index (S4) valueand a phase scintillation index (σ_(φ)).
 13. The method of claim 8,further comprising: assigning a first weight to a first selectedobservation associated with the satellite signals transmitted by theselected GNSS satellite in response to determining the pierce pointfalls within the boundaries of the scintillation bubble; and assigning asecond weight to the first selected observations associated with thesatellite signals transmitted by the selected GNSS satellite in responseto determining the pierce point does not fall within the boundaries ofthe scintillation bubble.
 14. The method of claim 8, further comprising:assigning a first weight to a first selected observation associated withthe satellite signals transmitted by the selected GNSS satellite inresponse to determining the pierce point is at a first location withinthe boundaries of the scintillation bubble; and assigning a secondweight to the first selected observations associated with the satellitesignals transmitted by the selected GNSS satellite in response todetermining the pierce point is at a second location within theboundaries of the scintillation bubble, wherein the first location andthe second location are different locations.
 15. A rover, comprising: aprocessor and a memory, the processor configured to: receive, from aserver, a phase scintillation map including one or scintillationbubbles; determine if a pierce point, associated with a selected globalnavigation satellite systems (GNSS) satellite in view of the rover,falls within boundaries of a scintillation bubble of the one or morescintillation bubbles of the received phase scintillation map; andassign a first weight to a selected satellite signal observationassociated with satellite signals transmitted by the selected GNSSsatellite in response to determining the pierce point falls within theboundaries of the scintillation bubble, or assign a second weight to theselected satellite signal observation associated with the satellitesignals transmitted by the selected GNSS satellite in response todetermining the pierce point does not fall within the boundaries of thescintillation bubble.
 16. The rover of claim 15, wherein a location ofeach scintillation bubble on the phase scintillation map is based oncoordinates of one or more base station pierce points and one or moreassigned index values.
 17. The rover of claim 16, wherein the one ormore assigned index values are based on at least one of an amplitudescintillation index (S4) value and a phase scintillation index (σ_(φ)).18. The rover of claim 15, wherein the processor is further configuredto: exclude, in response to assigning the first weight to the selectedsatellite signal observations, the selected satellite signalobservations when performing position calculations.
 19. The rover ofclaim 15, wherein the processor is further configured to: prioritize, inresponse to assigning the first weight to the selected satellite signalobservations, particular satellite signal observations associated withone or more other GNSS satellites over the selected satellite signalobservations when performing position calculations and when the firstweight is assigned to the selected satellite signal observations. 20.The rover of claim 15, wherein the first weight assigned to the selectedsatellite signal observations is based on the pierce point being locatedat a particular position within scintillation bubble.